1. Field of Invention
This invention relates to a self-modulating, remote, moving target detector for use in intrusion alarms, vehicle detection, and remote speed and distance measurement, and that includes a continuous wave radar transceiver in which the same frequency used for the radar transmission is modulated in a continuous manner in order to transmit radar data concerning a moving target to a remote receiver located away from the radar transceiver. The primary radar signal becomes the information carrier concerning the moving target, which is received remotely in order to activate an alarm or a display system showing the moving target. The system and method can be utilized with any frequency from audio to light, with RF and microwave of primary interest.
2. Description of Related Art
Radar is a system consisting of synchronized radio transmitters and receivers that emit radio waves and process their reflections for display for detecting and locating objects. Using the Doppler effect, radar can be used to detect moving targets. Typically the radar sends out a pulse of energy, shuts off and listens for the return echo from the same transmitter in which there is a receiver also. Based upon the Doppler effect, it is know that if the source of oscillation or the observer of oscillation is in motion, there is an apparent shift in frequency that can be measured at the receiver.
The use of the Doppler effect to detect moving objects in a microwave system to safeguard property against burglary and vandalism has been shown in U.S. Pat. No. Re. 25,100 issued to Chapin, where a personal intrusion device using microwave energy is continuously radiated throughout an area to be secured. The energy returned by a moving intruder is detected to produce the indication of his presence. Reflections obtained from fixed objects do not give rise to a change in phase or an apparent change in frequency and therefore have no effect on the system. Thus this system is capable of discriminating between moving and stationary objects. U.S. Pat. No. 4,215,341 shows an intrusion or movement detector that includes an oscillator for generating a radio signal, an antenna for transmitting said radio signal into an area to be surveyed by said detector which does not use a traditional receiver. The device in the ""341 patent uses the variable radiation resistance relative to the positional movement of objects in a variable loading on the generator, and a monitor for monitoring the variable loading for activating a signal or an alarm. U.S. Pat. No. 3,691,558 issued Sep. 12, 1972, shows a moving object microwave detection system that utilizes a plurality of transceivers that are all wired to a remote alarm system or monitoring station to detect human intruders. The system uses the Doppler effect in a conventional transceiver oscillator detector and amplifier system.
The present invention uses the Doppler effect for moving target detection, but is quite different in structure and operation than those shown in the prior art. The present invention provides a moving target detector for humans, animals, or vehicles, in which the primary radiating wave from the main transceiver is continuous (not pulse) and is itself modulated by the return detected frequency in the transceiver, which is continuously transmitted to a remote RF receiver at a remote location. It is desirous to have as little phase noise as possible in the primary oscillator used in the radar system. In the present invention, the oscillator is self-modulated by the frequency shift of the moving target, such that the radar signal that is being continuously radiated is the information carrier through the modulation caused by the moving target frequency exchange. A remote receiver continuously receives information concerning the moving target without itself transmitting.
A system and method for detecting moving targets such as human beings, animals, or vehicles for surveillance purposes that includes a radar transceiver that broadcasts a continuous wave from a first location, the radar transceiver also receiving a reflected radar signal from a moving target of a different frequency or phase and a modulating device within the radar transceiver to modulate the continuous radar wave as a function of the Doppler shift that is caused by the moving target. A different remote modulated wave receiver receives the primary radar transmission wave of the transceiver that includes modulated information about the moving target. The remote receiver includes demodulation circuitry and audio or video (or both) alarm and display to indicate the presence of the moving target.
The primary radar transceiver includes a voltage controlled oscillator that creates an RF continuous wave, an amplifier for enhancing the RF output and a power divider. The output of the power divider includes a circulator connected to the transmitting and receiving antenna. The power divider also has an output to a mixer which is also connected to the output of the circulator. Thus the mixer receives the original RF signal from the power divider and the output of the circulator which includes the received radar reflected signal from a moving target.
A circulator couples signals reflected from a moving target received back from the antenna to the mixer but not to the power divider.
The mixer detects frequency and phase differences between the signal from the power divider and the output of the circulator which represents the reflected signal. The difference in the continuous oscillated signal and the received reflected signal (in phase or frequency) is then amplified and fed back to a high gain/low frequency amplifier and to the voltage controlled oscillator in which the received radar signal modulates itself with its own Doppler or phase detected signal. The continuous wave source of radio frequency energy emitted by the voltage control oscillator has thus become modulated by the detected frequency and phase differences in the signal reflected from a moving target such that the transmitted continuous wave contains information concerning the moving target itself.
The system thus includes a remote receiver that receives the transmitted radio frequency energy containing information processed on the moving target. Thus the remote receiver includes an antenna, an RF receiver which includes an analog or digital signal processor that extracts the Doppler information which goes to an audio or visual alarm or display system. The remote receiver site then receives passively continuous information concerning moving targets in the area without the use of a second transmitter.
The system and method can be used basically for any frequency from audio to light with RF and microwave being perhaps the most useful. Using the method of the present invention modulation is introduced in the radar signal oscillator that normally would be kept clean in order to transmit a single frequency. The end result of the present invention is that a continuous flow of analog information audio and/or visual is available at the remote receiver concerning a moving target without a transmitter.
The invention has use for remote intrusion alarms, vehicle detection and remote speed and distance measurement.
It is an object of the invention to provide a method and apparatus to detect moving targets such as personnel using a continuous wave radar transceiver and a remote receiver.
It is another object of this invention to provide a continuous wave radar system that modulates the radar signal oscillator with moving target information for detecting moving targets that eliminates the need for two transmitters for remotely detecting a moving target using Doppler principles.
Yet another object of the invention is to provide an improved system for detecting a moving target at a smaller size, lower cost, with less power consumption and increased reliability.
And yet still another object of the invention is to provide a remote target moving detector for use as a remote intrusion alarm, vehicle detection and remote speed and distance measurement device that can use any frequency from audio to light.